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Curb find. Previous owner said the battery worked for 4 years, then died. After charging it overnight, I see the the volt readings shown in the photos. So about 13v on both sides, but I can't get a reliable reading on the output connectors. The battery test shows it's fully charged.

I am a newbie so might be doing it all wrong, but in any case, how do I figure out what's wrong with the battery and what's the easiest and cheapest way to repair it? A new one costs ~$200 so not an option.

Thank you!

Those batteries are dead. They should read 13.8 volts when fully charged. If they are not properly connected to the mower terminals, you won’t get a reading. You can buy a new set of batteries for $100.

If those are lithium ion batteries, don't try to repair them. Don't even try to mess with them. They like to go nuclear if they short out or are damaged. Think very hot fire that may be hard to put out.

ILENGINE said:

If those are lithium ion batteries, don't try to repair them. Don't even try to mess with them. They like to go nuclear if they short out or are damaged. Think very hot fire that may be hard to put out.

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Those are SLA batteries, not lithium ion. They can leak acid, but not catch fire.

Unless you remove the small black and red wires from the battery and clean all the connections, you are not going to get good readings. Second, I don’t know what that part, labeled 100, is or if it will give you a false reading. It may be a diode, which you can test to see if it is good. I do agree that the batteries may be junk, but at the price of new ones I would want to be sure of my decision before replacing.

13 volts on each battery in series would give you 26 volts output. You are only testing one battery. But you would need to find the ampere hours rating on those batteries and buy a couple new ones, not necessarily the Worx brand. SLA batteries on Ebay are pretty reasonable and I've had good luck with them in various uses.

Rivets said:

Unless you remove the small black and red wires from the battery and clean all the connections, you are not going to get good readings. Second, I don’t know what that part, labeled 100, is or if it will give you a false reading. It may be a diode, which you can test to see if it is good. I do agree that the batteries may be junk, but at the price of new ones I would want to be sure of my decision before replacing.

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Roger that. That is a fuse, so if it is blown the voltage at the connector will be zero. It is not required, so the wire can be be directly connected to the battery terminal.

tom3 said:

13 volts on each battery in series would give you 26 volts output. You are only testing one battery. But you would need to find the ampere hours rating on those batteries and buy a couple new ones, not necessarily the Worx brand. SLA batteries on Ebay are pretty reasonable and I've had good luck with them in various uses.

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The fully charged voltage should be 15% above the nominal voltage, or 2 x 12v x 1.15 = 27.6v. So, neither of those batteries is good. WORX does not sell the individual batteries, just the completely assembly. They are 17ah, but 22ah gel cell batteries will fit.

Could be low voltage and resulting high current blew the fuse? Those are pretty powerful batteries for the size I'm thinking.

tom3 said:

Could be low voltage and resulting high current blew the fuse? Those are pretty powerful batteries for the size I'm thinking.

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Not sure how that could occur. The purpose of the fuse is to protect against a short circuit or ground fault in the mower. It also protects against the mower connectors somehow getting shorted. All WORX SLA batteries have them.

Wattage and ohms law. Decrease voltage, increase in amps to maintain wattage, increases resistance, heats up fuse. All assuming the batteries can still produce the amperage and those could probably do that enough to blow the fuse. Or not.

tom3 said:

Wattage and ohms law. Decrease voltage, increase in amps to maintain wattage, increases resistance, heats up fuse. All assuming the batteries can still produce the amperage and those could probably do that enough to blow the fuse. Or not.

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If the battery voltage drops too low, the motor simply will not run, and therefore will not draw any power. If what you said were true, every time your starter motor battery ran down, you would blow a fuse. Anyways, that is a 100 Amp fuse, so there's no way a motor working normally can draw that much current.

OK thank you everyone! This is good info for me for future. Sadly, I've decided to scrap the mower and recycle the batteries. Could not find replacement batteries online for cheaper than $200 so not worth it...

An unfortunately you have found the issue with the battery operated mowers. When you need batteries the replacement cost is almost the cost of a new mower.

ilyaz said:

OK thank you everyone! This is good info for me for future. Sadly, I've decided to scrap the mower and recycle the batteries. Could not find replacement batteries online for cheaper than $200 so not worth it...

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See my previous post #2. You can buy a set of new batteries for just $100, and they will be better than the original ones. I gave you a link to Amazon where you can buy them.

MowerMike said:

See my previous post #2. You can buy as set of new batteries for just $100, and they will be better than the original ones. I gave you a link to Amazon where you can buy them.

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I saw them when I did my earlier searches. Those wouldn't fit: too tall.