help put an extra battery in my cordless mower

I'm probably the last person in the state with a cordless mower, but I like it because of the low noise and lack gas, fumes, lots of parts that can break etc. I've always been able to do our entire 1/4 acre lot on one charge, provided the grass is dry, but I admit it tends to bog down near the end, and more so recently. (It's kinda heavy too.) Bought it in '97 --a Toro Carefree 24(v).
I have just barely survival knowledge things electric so I'm seeking your advice.
If I could get a 20% longer run time I'd be happy. I took off the lid of the mower. There are 2 12V batteries wired in series driving a 24V motor. There's a empty slot for one more 12V battery. The label on the batteries read: "Yuasa sealed rechargable lead-acid battery ylm 18-12 12v 17.2Ah voltage regulation 14.4-15.0V initial current 4.3A max".
I thought I would buy and install an extra 12V battery of similar amp/hours and form factor. (Found one at gotbatteries.com.) I'll wire the new one in parallel with the original two (keeping those wired in series).
I can't find much out about the internal charger (You plug this mower into a 120V socket to recharge.), but the charger is still going to see one 24V battery anyway, right?
Do you think my idea will work or am I missing something?
--wahzoo
PS. I called Toro (who no longer makes cordless mowers) and they "didn't recommend" my idea, but I believe they're just being legally careful. Also I'm gonna strap 15 lbs of barbell plates to the mower to test if I can tolerate the extra weight!
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I think that your idea will not work. Simply put, the batteries you have now are set up to behave like 24 volts. If you wire a 12 volt battery in parallel, it's going to try to dump the higher voltage (24V) into the single odd battery, and fry the second battery.
I'm guessing that the replacement battery was quite pricey.
Now, if you wanted you could get two garden tractor batteries at Walmart, and wire them in the same as the other ones (plus and minus and all that). They likely aren't the same size, though.
I had a battery booster pack from BJ's Wholesale club (for jumping car batteries) and the light got left on during the winter, and froze the battery. I got a garden tractor battery and moved all the wires and such from the jump pack. Oughta work. Right?
Only other difference, the garden tractor batteries are starting batteries, not deep cycle. I'd suggest either two new Yuasa batteries (simple replacement of the two you have) or mow the lawn in two days. Those sealed cells do get weak after a couple seasons. Brand new ones may well have the extra 20% you desire.
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Christopher A. Young
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wahzoo wrote:

you have 2 12 volt batteries wired in series to make a 24 volt battery?? if that is correct then adding a 12 volt battery parrallel i gonna give you something like this... 24 volts + 12 volts = 36 volts divid by 2 gives you 18 volts.. so you gonna loose power and not get 24 volts to the motor... why not just replace the two old batteries at a higher amp. hour rating and that should make it work longer... make sure the wheels turn freely and the blade is not full of cord/string around the shaft, that will show it down... a mower bought in 97 might just be on its last leg... any rechargable item i ever bought did not last very long.....
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wahzoo wrote:

Just on the remote chance this isn't a troll... If you connect a single 12v battery in parallel with a 24v battery (of which the two you now have is the equivalent), you will probably get an explosion, spewing battery acid and battery parts for a fair distance, blinding you and causing acid burns and lacerations to your upper body and face. What happens is that excessive current will flow through the three batteries, now in series, with one wired backwards, causing the electrolyte to boil, creating enough pressure to rupture the case of one or more of the batteries. You might get away with paralleling another set of two batteries, or one 24v battery, but there are precautions to be followed to equalize the charge state between the two sets of batteries. It is generally not recommended to operate a new set and an old set of batteries in parallel, anyhow. All in all, leave the thing alone.
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After mowing 3/5 of the lawn, you oughta sit down with a glass of water anyhow.
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Christopher A. Young
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snipped-for-privacy@hotmail.com (wahzoo) wrote in message
As others have pointed out, the third battery will not work as you need to keep the battery stack at 24V, something you cannot do with 3 12V batteries. 6 years is a very long service life for a lead acid battery (when was the last time a car battery lasted you 6 years?). Replacing only one will only help a little as both batteries have aged equally. Safest bet is to go with the exact replacement. Next safest, get a suitable replacement of the same Amp-Hour rating, so much the better if that lawn tractor at walmart fits the bill. If you decide to go with a higher amp hour rating battery, the charger may give you problems.
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Sorry, adding a third battery couldn't possibly work the way you want to wire it unless it was a 24 volt battery. Before you go looking for a 24 volt battery (and get stuck with having to determine if your charger will still work), however, I have some other suggestions.
Batteries will "behave" better if they don't get too warm - so perhaps a few 10 minute breaks while cutting will stretch the duty cycle a tad.
Another possible help might stem from the fact that some oxidation (was it oxidation, sulphation, or some other reversible chemical consequence, darned if I remember off the top of my head!) occurs with fast chargers - so if the charger that comes with the mower has an charge rate incompatible with getting the most from the batteries over time, a slow charge a time or three <s> per season might return some capacity.
To check this out, I would obtain a 12 volt slow charger (couple hundred milli-amps maximum charge rate) and use it for about 14 - 20 hours on each battery, ONE at a time. Testing is strictly a "proof's in the pudding" situation... .
Oh, the more work the motor has to accomplish, the more quickly the batteries get run down - so let me also suggest keeping the blade sharp and well balanced.
HTH
Stephen Kurzban
wahzoo wrote:

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How dumb. I wrote it bass ackwards. I meant that I'd wire the two original 12v batteries PARALLEL and then 3rd new 12v battery in SERIES with those, giving 24v.
So would that work? What's wrong with it if it doesn't?
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Well, now, if you wire the old + to the other old battery +, and wire the old battery - to the other old battery -, and then wire a combined - to the new battery + and then wire the old battery + to the machine, adn the new battery - to the machine.... now we're talking.
Say your old batteries are about half dead, then side by side they would just about equal one new battery.
I think you're on to something.....
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Instead of adding extra weight, and possible other issues you may have, why not buy TWO new batteries, and get all your run time back?

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