Goal Zero “Extreme 350” Battery Replacement

IMPORTANT Update January 9th 2021:

Readers, please note that I originally used a Mighty Max battery. However in December of 2019, Mighty Max changed their specs and the new batteries were too tall. We found that the Weize battery currently linked here on Amazon worked out fine. However just in the last month or so, some readers have indicated that Amazon sellers are shipping two different types of Weize batteries from the link we provide. Although the measurement specs on the product page appear correct, they may ship a battery that is too tall. We have yet to figure out exactly how to get the right battery from Amazon sellers. I do not currently have any info on how to ensure that you’ll get the correct battery. Review the latest comments at the bottom for more info. Please comment if you find out anything helpful.

Update as of Mid January 2020:

Katie, who has commented below on this article, indicates that she has tried the Weize battery and it fits.

Weize 12V 35AH SLA Deep Cycle AGM Battery

IMPORTANT Update as of December 18th, 2019:

A couple of readers have alerted me to the fact that Mighty Max has changed their specs slightly and the batteries are now too tall to fit in the internal bracket in the Goal Zero unit. (Please see the comments section for details.) I have not yet purchased a new battery to try with my own Extreme 350s, but I will be doing so in the near future since my Ritar batteries have finally given up. Once I do so I will change the article to reflect the new batteries I’m using. (See the measurements I’ve put in the comments section. The critical measurement is the height.) For the time being and based on my research I believe this Weize battery will work.

Update as of October 24th, 2019:

I’m pleased to announce that, two years later, the Mighty Max replacement batteries (SLA) are still going strong at full capacity… even after a very lengthy period of storage with no re-charges. Read all the way through to the bottom of the article for all the details.

Originally published July 1, 2017

Goal Zero certainly has a positive product lineup. They’ve been refining their offering for the past several years. The flagship mobile power pack they currently offer is the Goal Zero Yeti Lithium Portable Power Station. You can find out more about this batteries and current costs here: Goal Zero Yeti

Goal Zero Extreme 350
Extreme 350 disassembled

When Goal Zero launched it’s initial product lineup in 2010, the flagship powerpack was the Goal Zero Extreme 350. Essentially they provided a good looking and functional case around the RITAR RA12-33 gel battery. It’s a 33 amp hour battery. These batteries are generally used in applications like wheelchairs and uninterruptible power supplies (UPS). The Goal Zero enclosure is a stackable and sturdy design that gives the user a solid carry handle, Anderson Power Pole connectors, a charging port, slots to attach the 400 Watt Goal Zero power inverter, access to fuses, a simplified charging port and an intuitive power level meter that was easily understandable by pretty much anyone.

Here’s the problem. These batteries are notorious for going bad. I imagine that most of the units sold have simply sat and discharged and then sulphated over time. They are difficult to revive and simply can’t be recharged well with the provided AC wall charger.

My father and I each acquired two Extreme 350 units about the same time, 2011-2012 ish. He stuck his in the garage and never paid any further attention to them. I checked on mine and realize that they discharged pretty rapidly according to the on-board power meter. Even if left plugged in they seemed to not keep a charge very long. As I was somewhat concerned about that, I partially disassembled mine by disconnecting the internal batteries from the top part of the case which contains all the electronics and connections. From then on I stored them without the top on my workbench next to my other batteries. I’ve regularly used a Battery Minder charging unit to re-charge and maintain these batteries. five or six years later, my RITAR RA12-33s seem to hold a consistent 12.7 – 12.8 volts over time.

Meanwhile I recently discovered that my father’s Extreme 350 batteries were dead. They were deader than dead. The power meter was blank. I took them home and over several weeks I tried everything to revive the RITARs. I tried the Goal Zero charger. I used various other charging methods including my Battery Minder. I ultimately connected one of the bad RITARs with a good one in parallel to trick the charger into thinking they had voltage. This got the process going but ultimately “bulged” the battery. It was clear they were dead and dangerous.

I thought it would be a shame to waste these Extreme 350 cases. The enclosures are really solid. I like the idea even though it’s not the latest and greatest. I googled all over looking for a write-up of replacement options and “how-to.” Seeing none I made some measurements and took a small risk and ordered new batteries for my father’s enclosures.

It works!

Note as of Dec 2019. The Mighty Max may no longer fit the enclosure. It may be too tall. Please see the notes in the comments for measurements. Katie, who has commented below on this article, indicates that the Weize battery does in fact work and is the correct size. Weize 12V 35AH SLA Deep Cycle AGM Battery

The battery I originally used was the Mighty Max: ML35-12 – 12 VOLT 35 AH SLA BATTERY. I’m told by readers that the current version is slightly too tall. I’m sure there are others out there that have the same dimensional specifications that you could use. See the comments for the exact dimensions of the enclosure.

Mighty Max: ML35-12 - 12 VOLT 35 AH SLA BATTERY
Mighty Max: ML35-12 – 12 VOLT 35 AH SLA BATTERY

Here are the tools you’ll need:

  • 4mm Hex key
  • 3mm Hex key
  • #1 Phillips Screwdriver
  • 10mm inch box end or combination wrench

How to replace the battery – Goal Zero Extreme 350:

  1. Remove the handle using the 3mm hex driver
  2. Lift the top up carefully
  3. Slide the wrench in and loosen the terminal bolts. Pay attention to not touch the wrench to both terminals at the same time.
  4. Remove the side screws using the 4mm hex driver
  5. Carefully pop the plastic sides off
  6. Turn the battery on its side and remove the four Phillips head screws from the base
  7. Detach the battery from the base
  8. Remove the metal supports from each side and place them on the new battery
  9. Re-attach the base to the metal side supports. The Mighty Max fits perfectly.
  10. Replace the plastic sides and attach with the 4mm hex driver. Don’t force anything too hard.
  11. Connect the top to the new terminals.
  12. Tighten the terminal bolts. Pay attention to not touch the wrench to both terminals at the same time.
  13. Set the top in place. Pay attention to replace the heat sensor to the side of the battery. Make sure you are not crushing any wires or circuit boards etc.
  14. Re-attach the handle using the 3mm hex driver.
RA12-33 vs ML35-12 Terminals
RA12-33 vs ML35-12 Terminals
Extreme 350 Power Meter
Extreme 350 Power Meter
The Mighty Max Fits Perfectly
The Mighty Max Fits Perfectly
Extreme 350 Heat Sensor
Extreme 350 Heat Sensor


Why they discharge so quickly

I’ve done some minimal experimenting with the Extreme 350 by comparing the two new ML35-12s side by side. I believe that the design flaw is that the Goal Zero power meter is always on. It’s got a constant drain on the battery. After replacing the batteries I removed the fuses from one of them, thus disconnecting the power meter and essentially rendering the whole thing inoperable. I set the two Mighty Maxes next to each other and compared voltages over several days. The one that was disconnected remained constant while the other lost voltage. It’s my intention to check on them after a few months and see where they’re at.

The Solution?

Store your Goal Zero Extreme 350s with the fuses removed. You can set them loose inside the fuse compartment. Then check the voltage every few months. You can do this with a volt-meter or just plug the fuses back in and use the on-board meter.

Check Amazon for the latest pricing on a replacement battery. As of January 2020 I am recommending the Weize battery versus the Mighty Max. Mighty Max recently added about a quarter inch to the battery’s height. Current prices may vary. … anyway two years ago after re-assembling them I gave them back to my dad as a Father’s Day gift. He seemed mildly impressed. 😉

Click the Amazon link to the left to purchase this replacement battery. FREE SHIPPING!

Update on Voltage September 2017

As of September 2017 the new Mighty Max batteries are holding at 12.8 volts. I would expect they won’t need to be recharged for another several months.

Update on Voltage October 2019

As of October 24th, 2019 I’m happy to report that these Mighty Max batteries are still holding strong. My dad is still only mildly impressed. But I, on the other hand, am very happy to see this as my original gel batteries seem to have run their course. They’re about 7-8 years old now and not holding voltage very long. I need new ones.

I stuck my dad’s two “Mighty Max” units in his downstairs storage closet, and I failed to recharge them since my last update in September 2017. Yes, procrastination. I am certain he never touched them either. I did leave them with the fuses pulled out. So there was no drain on the battery. The storage closet temperature is probably 60-65 degrees Fahrenheit.

About a month ago I brought them home to check on them and recharge them. The batteries read 12.59 and 12.63 volts. Based on my understanding of lead acid batteries, that means they both still held about a 90% charge, 12.7 volts being considered fully charged. So had there been an emergency, my parents could have counted on using these batteries as is without any trouble.

I decided to experiment with charging methods. I used the supplied Goal Zero charging cord for one and my BatteryMinder battery charger for the other. The Goal Zero charger decided that the battery, currently holding just over 12.6 volts, was fully charged after being connected for about 10 seconds. It was difficult to gauge but it appeared to me that it would charge at about 13.4 volts for a very short period of time. It then reverted to a trickle charge of 12.88 volts approximately. This was disappointing. I assume if left connected for days I could get that battery to top out about 12.8 volts.

The BatteryMinder charges at around 13.4 volts also. But it brings the battery to a much higher level than 12.6 volts before going to it’s trickle mode. I kept it on the first battery for about six hours. Then I moved it to the second one for the same amount of time. After about a day, they are both holding at 12.93 volts. I assume that will fall to around 12.8 volts in the few days.

By the way, if you’re not using the Goal Zero supplied charger you’ll have to take the top off of the battery enclosure as explained in steps one and two above. IMPORTANT: Be very careful. Leave the fuses OUT if you decide to disassemble it and use a 3rd party charger. This allows you to bypass the charge controller that is built into the unit. Fortunately I’ve only had to do this once in the last two years to keep these batteries in shape.

I really like the BatteryMinder battery charger. I’ve got a couple of them and use them regularly on my RV batteries and other large (i.e. auto-size etc.) batteries. They’re kind of pricey but pretty intelligent. Maybe I’ll do a review on the site about them at some point, but for now you can check Amazon for the reviews which are quite positive.

Here are some other Goal Zero (and BatteryMinder) products that are related which you might be interested in:

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Moses Roni

Moses Roni

Prepper, commenter, diy'er since the '90s. -- "Enviest thou for my sake? Would God that all the Lord’s people were prophets, and that the Lord would put his spirit upon them!"

28 thoughts on “Goal Zero “Extreme 350” Battery Replacement

  • May 1, 2019 at 10:22 am

    Thanks for this info! Very helpful!!

  • August 24, 2019 at 12:45 am

    Was gifted an Extreme 350 that had a battery that was deader than Hillary Clinton’s presidential chances. Ordered up the battery from Amazon, followed the instructions, and everything worked fine. Thanks for posting this…it really made a difference.

  • October 8, 2019 at 5:35 pm

    Thanks also for the info – I am ordering my batteries now for 2 of my olders Goal Zeros.

  • October 14, 2019 at 8:15 am

    Thanks! I got the battery from your link and it works! So glad to have it working again. I’ve used my GoalZero in a power outage before and had my internet equipment and laptop plugged into it. I was still connected and could watch movies without power.

  • December 7, 2019 at 12:27 pm

    I got the battery in the link (the ML35-12) but I’m having some trouble getting the GZ Extreme 350 bracket to fit around it.

    I’m not sure if something’s changed with the battery or if I’m missing something simple…

  • Moses Roni
    December 7, 2019 at 12:56 pm

    I just went and measured the original battery (the Ritar) and compared it with the current specs on the Amazon page for the ML35 and it appears to me that they’re still the same height, width and length.

    If you compare the old and new battery side by side are they the same size? If not what’s different? Let me know.

    If the batteries you have are same size, maybe I can post another picture of the battery just with that internal bracket on it and that might help.

  • December 18, 2019 at 4:05 pm

    Having same problem with the bracket. When sitting side by side, the ML35 is about 3/32″ taller. Thinking about shaving a little off the bottom of the battery.

    • Moses Roni
      December 18, 2019 at 7:14 pm

      Louis – Thanks for the update. Let us know what you decide to do and if it works out ok.

      Katie – Thanks for alerting us to the problem.

      My apologies to anyone that has a Mighty Max that is too large. They have changed the size of the battery very recently. I just went out and measured the bracket and Ritar battery as closely as possible. I was able to use a caliper on the height and width but not the length as it is too long for my caliper. The critical measurements are height and length as far as the internal bracket is concerned.

      My Ritar Battery Specs:
      Width: 5-9/64″ (5.14 inches … 131cm)
      Height: 6-3/32″ (6.09 inches … 154.8cm) (not including the terminals)
      Length: 7-5/8″, 7-11/16 at the bulge (7.63 inches … 193.7cm)

      My Bracket Specs:
      Maximum Inside height: 6-7/64″ (6.11 inches … 155.2cm)
      Maximum Inside length: 7-23/32″ (7.72 inches … 196.09cm)
      I do not think a 7-3/4 inch length battery would fit.

      I’ll be updating the article shortly to alert new readers and provide some new battery options that appear to fit.

      Thanks again for your comments.

      • January 7, 2020 at 2:23 pm

        >Katie – Thanks for alerting us to the problem.

        No problem! Just wanted to drop a quick reply to share that the Weize LFP1235 fit in the Extreme 350 bracket perfectly.

        If you end up with a too-large battery you can’t return, you can toss it in a battery box and attach an AP cable and chain it off the 350 so it doesn’t go unused.

    • November 11, 2020 at 4:32 pm

      What did you finally do to fix the very slight height problem of the battery? I am having the same problem…it fits, but the handle screw posts are facing toward the outsides of the battery just a tad and I don’ think the screws will go in properly. Thx for your help…Heidi

  • May 21, 2020 at 12:08 pm

    I’m just writing to confirm that Moses and Katie are absolutely right. The Weize LFP1235 battery fits the GoalZero perfectly. Just be careful, as Moses says, when replacing the top. Make sure you’re not crushing the wires or circuit board when you reattach it.
    Quick question for Katie… what is an AP cable, and how to you chain the GoalZero to other 12v batteries? BTW, I’ll be recharging the GoalZero with a 100w Renogy solar panel and controller.
    Thank you Moses, for this tutorial.

  • September 23, 2020 at 4:20 pm

    Thanks Moses and Katie. I just replaced my yeti 350 battery. Quite a drama. Goal zero was out of stock. Spent half a day at Batteries Plus trying every battery they had. It’s bizarre that a company selling batteries like Goalzero doesn’t factor in replacement. It shouldn’t be this difficult!

    Anyway I found you and ordered the Weize battery. It fits!! Yay! Thank you for the advice and the tutorial. I was beginning to think I had a very pricey paperweight!

    Am replacing my yeti 1250 as well. A Duracell fits fine. A little short on length but the stabilizer bar holds it in place. That I could buy at Batteries plus. I do hope that Goalzero is aware of these conversations and will be more mindful about helping us replace batteries going forward. These are supposed to be ecologically smart to own. I would think being able to replace the batteries would be step one.

    • October 13, 2020 at 8:08 am

      I just yesterday replaced the Yeti 1250 battery–$299 at Batteries and Bulbs YIKES ! I will not let it completely discharge again. That’s the price of neglect. I am going to purchase the battery for the 350 today. No more neglecting my batteries; it’s a very expensive learning curve!

  • November 9, 2020 at 6:02 pm

    Seeing as how this post was updated recently and comments show that the Weize battery fit their extreme 350, I am disappointed to report the Weize does in fact NOT fit the extreme 350 (at least not anymore). Kinda irritating that someone just did this a month and a half ago and Weize went and changed the form factor of their 35Ah batts. =/

    • Moses Roni
      November 9, 2020 at 6:49 pm

      CJ – Sorry to hear that. Can you tell us what the dimensions are of the Weize battery you received? The current Amazon pictures (for the Weize battery) show dimensions that should work. (But that doesn’t mean their picture is accurate if they’ve changed the battery.)

      • November 10, 2020 at 5:30 pm

        I got some more info. It looks like I was sent an incorrect model number of the battery. I reached out to the seller. I received a LP1235 and not the LFP1235. They were responsive at first but I haven’t heard back from them. The battery is just a tiny bit too tall for the steel cradle inside the GZ350. I am hoping and assuming that the model with ‘F’ in it will be the correct size if they can still get me one. I may keep this battery for chaining to the GZ350.

        • November 11, 2020 at 4:48 pm

          The SKU on the box says QS12-35-T
          On the battery it says TL1235(12V35AH/1OHR
          It’s a bit too tall, less than an 1/8 inch.
          They are closed today, will phone them tomorrow.
          I definitely ordered from the Amazon link above.

          • November 12, 2020 at 11:59 am

            I haven’t checked the box, but on the battery, mine looks almost identical to the pictured product from the link at top of this article, the only difference is the battery in my hand has the model number without the F.

            I also heard back from them again, same seller as above link, they say:

            “We apologize for this inconvenience, we checked our tech department, our battery size is similar, 0.3 inch difference at most, but the warehouse is shipped randomly. We are willing to give you $10 refund as compensation to keep it, is it OK?
            Thanks a lot
            Powermall customer service”

            I’m torn, it seems to be a good battery and came with proper charge, but it doesn’t fit. I could keep it and chain it to the GZ350 when I am able to find the proper battery for it.

            Does anyone have other recommendations for the correct battery model to replace the one inside my GZ350? I guess I could always trip 1/16 inch off the edge and top where the frame is supposed to sit as the top of this battery is not also the sealed compartment into the battery itself. Hmmmmm…

          • November 12, 2020 at 12:01 pm

            Ooops, meant *trim* the plastic on top of battery.

  • December 5, 2020 at 7:02 pm

    Replaced the battery now, it fits great. Excellent advice in this post!. Since my attached 350 Extreme UI inverter which had the outputs has bit the dust. Has anyone had the same situation and came up with an idea of how to have ways to charge DC devices and via USB with the Yeti 350? I figure using the Anderson in some way?

  • January 7, 2021 at 12:10 pm

    I found I was also hit with the Powermall “warehouse shipped radomly” wrong battery. I ordered the LFP1235 in Dec 2020 and received the LP1235 (the one that is too tall for the case to fit). So since we have not other battery that has been identified that will fit I’m stuck with an empty GZ 350 case.

  • January 9, 2021 at 12:09 am

    Firstly thank you so much for this POST. Invaluable for me to get one of my Goal Zero’s working!!!

    I have two Goal Zeros. I ordered the Weize 12V 35AH battery from Amazon that Katie recommend with the flexible rubber handles that you can remove and it worked perfectly on the height. The box says SKU: QS12-35-T (the -T is very important).

    Because that worked so well I wanted to fix my other Goal Zero a few months later and ordered the exact same battery from Amazon from the same vendor. The picture on Amazon still looked the same as last time. However they look different as the second one has hard plastic handles that fold up like those hand-carry shopping baskets at WalMart. The box reads QS12-35-A. The -A is too tall for the Goal Zero metal case inside. I complained to the seller and they offered me 20% off to keep it. I probably will so that I can use it as an external battery to my first Goal Zero to double the capacity.

    So, I am not sure how to actually get the unit that I need so will try to fight with Amazon Seller – Powermall that is listed as Brand: WEIZE when you are looking at the web page. 50/50 chance you will get the right battery:

  • February 17, 2021 at 5:21 pm

    Thank you for the guide. Just used this to replace mine with the Weize battery linked above. Worked like a champ, and easy to swap out.

  • March 5, 2021 at 12:09 pm

    I just replaced with the Weize 12V 35AH Battery Rechargeable SLA Deep Cycle AGM Replace 12 Volt 33AH ordered from Amazon 2/27/21 and received 3/4/2021.

    Dimensions are spot on and thanks to your clear instructions swapped out and replaced in less than an hour.

    I bought my extreme 350 in summer of 2011 and had occasion to use it in January—Goal Zero’s inverter unit—and the power metere readings were whacked out. Did a search and found your article thanks again.

    Tom O’Connor

    • April 24, 2021 at 12:39 pm

      Just took my cage up to Batteries +. Too high by a silly millimeter.

  • April 9, 2021 at 4:48 pm

    I struggled to figure this out on my own a few years ago. I was an early adopter with goal zero, with a 150 a 350 a several briefcase panels. I have upgraded to a yeti 150 for camping and tossed the 350’s inverter. But the 350 straight to the powerpoles work well. I was thinking about a lithium battery swap.

  • June 29, 2023 at 6:50 am

    I know this thread is old, but I just wanted to chime in because if anyone else like me still has a 350 at this point, chances are the battery is dead or dies quick. I took the chance with the Weize battery linked from Amazon that has had mixed reviews. Here is that link again:


    The description is correct showing it should be an LFP1235 what everyone says fits perfect, but the images are of a TL1235 that some say don’t fit. I took the chance anyway, opened it up, and found I received a TL1235 thinking dang, it won’t fit, but I took my goal zero apart anyway to see.

    Well, the TL1235 I got fit perfect, and the simple instructions were great! The only thing not listed in the instructions is I took the fuses out before taking taking apart just in case. Thank you!!

    Images: https://imgur.com/a/435lTlr


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