Understanding Cordless Mower SLA Battery State

I have a cordless lawn mower with 2 12V sealed lead acid (SLA) batteries. The batteries are not charging properly, but what I am trying to understand is why when I test the batteries voltage without any load they read a posi tive voltage, but when I pull the switch (which would turn the motor on if there was enough charge) the voltage goes negative.
Does this suggest any additional problems with the mower or is that somethi ng normal?
Thanks, Jeff
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On 9/15/2013 11:23 PM, snipped-for-privacy@gmail.com wrote:

How old is the mower and/or batteries? The batteries only last so long and will fail prematurely if not properly cared for. ^_^
TDD
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I have a cordless lawn mower with 2 12V sealed lead acid (SLA) batteries. The batteries are not charging properly, but what I am trying to understand is why when I test the batteries voltage without any load they read a positive voltage, but when I pull the switch (which would turn the motor on if there was enough charge) the voltage goes negative.
Does this suggest any additional problems with the mower or is that something normal?
Thanks, Jeff
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One or more of the cells is bad (likely high internal resistance due to sulfating). There are somethings you can do to reverse the problem but unless you know what you're doing thoes are unlikely to improve the situation.
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I have a cordless lawn mower with 2 12V sealed lead acid (SLA) batteries. The batteries are not charging properly, but what I am trying to understand is why when I test the batteries voltage without any load they read a positive voltage, but when I pull the switch (which would turn the motor on if there was enough charge) the voltage goes negative.
Does this suggest any additional problems with the mower or is that something normal?
*Sounds as though the batteries are failing. To confirm, you can take them to a place that services cars and have them test the batteries.
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On 9/16/2013 2:52 AM, John Grabowski wrote:

More details. Assuming the batteries are in series... If you turn on the switch and BOTH batteries measure negative, you've discovered something new. If only one goes negative, that's the result of the other battery.
Bottom line is that you need new batteries. They're sulphated and they ain't comin' back.
Problem with most garden tools powered by lead-acid batteries is that they sit in the garage over the winter without charge and sulpahate themselves to death.
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Perhaps we could organize a tool exchange with Chile and Argentina, so that they could use power tools during their summer and we could use them during ours.
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On Monday, September 16, 2013 2:15:46 PM UTC-4, mike wrote:

The batteries are in series, and only one goes negative when I apply the lo ad.
Actually, I kept the charger on them all the time - but I recently learned that the charger sucks and is prone to over (or under - depending on who yo u ask) charging. I've seen some videos on YouTube on restoring a SLA by tr eating it like a regular lead acid battery that you can top up with distill ed water - but I don't think I want to take the risk popping the thing open and having sulfuric acid spray everywhere.
I also don't want to spend another $100 to replace the batteries, but I gue ss that's probably my cheapest solution...
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typical battery failure, they dont last forever. 2 to 3 years at best, and shorter if they sit uncharged. lead acid self discharge over time.
you could charge them out of the mower for a day or two, and then have them load tested....
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