what voltage is lower limit for stored battery?

If it's a lead-acid battery, drain it and store it dry, then refill it when you need it.

If it's a sealed battery, use a battery tender on it.

--scott

Battery Tender gets my vote.

Very good stuff (but not cheap)

Harbor Freight has a cheap version that has also given me good service.

Under $10 and often on sale for much less than that! Vaughn

I have this unit

That one should be fine (it may even be a rebranded Battery Tender). Just connect it to your battery and forget about it. There is no particular need to disconnect it as you should for any "dumb" charger.

Vaughn

how about my original (in subject) question?

is the lower limit 13 v, 12 v or something else?

is the limit different form AGM vs lead-acid type?

The lower limit is zero. Not sure what you are looking for though.

dont think a lead-acid can be at zero and still successfully brought back to

13.5 v or better

same with AGM type

could be wrong on both counts, thus am asking.

If you care about the battery, don't let it ever drop below 13.5V at all. Every second that it spends at less than full charge is wearing the battery out faster than the same second spent at full charge. That is why battery tenders exist.

--scott

I do not profess to be an expert of battery charging but have a set of deep cycle flooded lead acid batteries (4 x 6 volts) Trojan T 105 which in series is 24 volts. The batteries are 250 ampere hours.

I do not float charge them but allow the voltage to drop to 25.2 (or 12.6 volts for a 12 volt system) and the charge them.

I charge them up to around 30 volts that allows around 1.5 amps to trickle in. More often than not I will begin the recharging when they get down to

25.3 volts

In essence I charge them around once every 2 weeks and for around 10 hours at a fairly low amperage. They start charging around 5 or 6 amps tapering off to the 1.5 amps.

Last time I ran the charger was a week ago and the now have a voltage of

25.6 volts. There is no power being drawn from them.

A fully charged battery is around 12.7 volts for a 12 volt system and around

1. 4 for a 24 volts system with no charger running and allowing time for the batteries to stabilize after a charging

My charger is a 24 volt 40 amp simple charger, just a transformer and rectifiers. Yes I know there are automatic chargers, I had one and it broke down and the cost is considerable to replace it. This one just lasts and lasts.

The batteries are there for emergencies to supply 240 volts via the inverter. They are hardly ever used and have never been run down to even 1/2 their charge.

They are at least 2 years old. I noticed yesterday some corrosion on the terminal so looks like I need to clean them. It is also about time I checked the water levels.

I hope this is of some small help to you.

In general terms is seem that sulfation takes place once the battery is less than fully charged, and the lower the charge the more sulfation takes place and that is what ruins many batteries, hence I attempt to keep my batteries near fully charged.

yes, that helps. the batteryminder plus is specifically supposed to provide a pulse with 1 amp max when in maintenance mode. it charges the battery to max, measures that no more is possible and automatically switches over to maintenance mode, thus removing sulfation from the surface plates. at least that's what their literature states.

I have read about these de-sulfation units and have always wondered if they actually work?

Be interesting to see of anyone comes up and says they do.

12.65v is a fully charged Lead acid battery 12.45v is State of charge of 75%

So your keeping your battery over 75% charged by keeping the voltage above 12.5v, which should be fine.

For AGM I would consult the Mfg.

Cheers

It won't be me. I have always been very suspicious of any gadget or magic potion that is supposed to bring batteries back to life. I have never found any to be worth my time. Pulse de-sulfation may, or may not, extend the life of a battery, but I am particularly sceptical of any claims that they will "repair" a bad battery. (Others may have other opinions)

On the other hand, purpose-made lead-acid battery maintainers are wonderful money & battery saving gadgets.

Vaughn

Good advice. The Hawker Cyclon manual says to recharge when the cells drop to ~2.0V, and the discharge limit is ~1.5V. That's 12V and 9V for you young ones.

I'm not kidding. A Subway foot-long costs $6.81 with tax, I give $7.01, they all look very confused.

jsw

My Smart Charger (12 volts) has a built-in desulfate cycle. I have to admit that I have seen some improvement by running it for several sessions (24 hours each) on a bad deep cycle flooded battery. But I sure could not get it to recover a battery that was sulfated from being undercharged. So yes, I was able to get the SG up a little higher, but no, the battery was still not usable (in any practical sense).

12.5 volts sounds pretty darn close to what I think it should be. Keep in mind a trickle charger will probably only bring it up to 13.5 or 13.6 volts. That is fine for *maintaining* the battery but when you are charging it the voltage should be brought up to about 14.5 (this varies a little with manufacturer so ask them) and held there until the specific gravity reaches 1.280 (or close to that) on ALL of the cells. This can take some practice but after a few times you'll have a pretty good idea how long it will take. Occasionally (every 30-45 days if you are using the batteries) they should be brought up to about 15-15.5 (equalize) volts and held there for perhaps 30-60 minutes or until all of the cells are very even. This can also take some practice and you do not want to let the batteries get hot or exceed 60 minutes which is the upper limit IMHO. Sometimes, with sulfated batteries, you may need to equalize a little over several days to get them nice and even. Most battery manufacturers seem to be very happy to supply the voltage/SG info that you need.

Yes. Use one.

Most large UPS systems and big lighting charging systems now use the same process.

--scott

They will not repair a bad battery. Once there is gunk on the plates and the battery resistance has started to climb, the battery is dead.

The pulse desulfation is a typical feature of the battery maintaining devices, and they prevent sulfation from happening in the first place.

--scott

Apples and Oranges there Dufus.... Your Cellphone battery is either Lithium, NiMH, or Nicad.... None of these has any Sulfur included in it's Chemistry. SO, your resurrecting your Cellphone Battery has NOTHING in common with a Sulfated Lead Acid Flooded Cell Battery..... which IS the topic of conversation, here....

Apparently, you are just a minor Moroooon... (Bugs Bunny Definition)