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

On 9/15/2013 11:23 PM, wrote:
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


How old is the mower and/or batteries? The batteries only last so long
and will fail prematurely if not properly cared for. ^_^

TDD

wrote in message
...
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

{{{

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.

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.

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....

On 9/16/2013 2:52 AM, John Grabowski wrote:

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.

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.

On Mon, 16 Sep 2013 11:15:46 -0700, mike wrote:

On 9/16/2013 2:52 AM, John Grabowski wrote:

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.

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.

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.

On Monday, September 16, 2013 2:15:46 PM UTC-4, mike 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.

The batteries are in series, and only one goes negative when I apply the load.

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 you ask) charging. I've seen some videos on YouTube on restoring a SLA by treating it like a regular lead acid battery that you can top up with distilled 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 guess that's probably my cheapest solution...