PowerSwitch

I have a 75AH leisure battery.

It seems to be deadish - although maybe only used once in the last say 3 years.

I have charged it a few times during that period ... but charging it now doesn't do much.

Is that possible? Is has my charger failed?

My understanding is that they lose their storage capacity if not used. So although you have charged it, if you have not discharged it then it might be dead.

I think you find that batteries in UPS systems die pretty quickly under normal circumstances, for this reason.

If a lead acid battery is left on the shelf completly unused it will slowly run down due to self discharge, becoming initialy less useful, and eventualy totally useless. For this reason, lead acid batteries should be either obtained to order, or purchased from a supplier who has a good turnover.

Self discharge may be avoided by charging the battery, every few months as a minimum, every month would be better.
This will avoid any damage due to self discharge, but remember that the cheaper types of battery only last about 3 to 5 years.
Failure after 3 years is therefore probable, especialy as the battery may have been up to a year old when you purchased it.

Measure the voltage of the battery, if below 10 volts it is probably useless, though it is worth trying to charge it, just dont raise your hopes.

If you have any reason to doubt the charger, connect the charger to the battery, turn it on, and again measure the battery voltage with charger connected. It should increase, perhaps to about 13/14 volts.

Some types of charger dont work if the battery voltage is very low. In this case an initial charge direct from a PV module, or a cruder type of charger is worth trying. Remember though that a battery at such a low voltage is probably not worth charging.

Nickel Cadmium batteries may benifit from regular use, but with lead acid types I believe it to be an urban myth.
The batteries in cheap UPS units have a short life because they are cheap batteries initialy, and are often used in a warm enviroment and therefore overcharged. (the correct charging voltage for lead acid batteries is lower at higher temperatures. Large good qaulity chargers and UPS units measure the temperature and adjust accordingly. I doubt that a £49.99 UPS does this)

Better batteries can last as long as 25 years, but are very expensive.

Crude home made lead acid batteries can last decades, but will be of vast physical size for a decent capacity, and therefore expensive in materials.

I have a high performance charger ... I use the FAST CHARGE option rather than the TRICKLE CHARGE option ... was that a mistake?

You can't stop the chemical reaction. Trickle charge is the way to sustain longer battery life with lead acid once they're fully charged.

I've recently starting getting involved in UPS maintenance for a large Scottish bank, we renew the cells every 5 years regardless.

You need to 'equalise the potential' plates by removing the sulphur from their surface -- http://en.wikipedia.org/wiki/Sulfation; what the Yanks call 'desulfating' -- http://en.wikipedia.org/wiki/Desulfation.

You can buy fancy pulse chargers that do the job efficiently, or you use a charger which allows you to charge for a short period (20-30 minutes) at about 1 volt above maximum (say 15.4V instead of 14.4V) in order to burn the deposits off the plate (albeit that shortens the battery life more than pulse charging because you're removing metal from the plates).

Vortex wrote:I have a high performance charger ... I use the FAST CHARGE option rather than the TRICKLE CHARGE option ... was that a mistake?

Trickle charge might have been better, but I doubt that you killed the battery, it was probably dead already.

I don't think you can equalise charge lead acid batteries if they have a gel electrolyte.

Andy Hunt wrote:I don't think you can equalise charge lead acid batteries if they have a gel electrolyte.

True, the gel separates from the plate and the battery's knackered. But by the same token gel packs are not supposed to suffer the same problems because you don't get the stratification of the acid electrolyte -- it (well, it's supposed) to diffuse equally throughout the gel.

With gel cells you're usually using slower charge and discharge rates in any case -- which is why they're often used in small solar PV applications. I've never come across a gel "leisure" battery because, as they're more expensive and restricted in application, they don't work well on heavy charge/discharge cycles. I think they're most often used for marine applications because they're wholly sealed (standard SLA's can vent under heavy charging whereas gel cells have a catalyst to recombine the gases) and they don't have a problem with mechanical shock and/or being regularly turned upside down.

An equalising charge should indeed only be applied to flooded lead acid batteries, not to gel or other sealed types.

The equalising charge serves two purposes, firstly it ensures that all cells in a battery or series string become fully charged, and secondly it results in considerable gas being produced from the plates, the rising gas bubbles stir up the acid and prevent it reaching different strengths at the top and bottom of the cell.

The voltage during an eqailising charge may be high enough to damage certain loads and precautions should be taken.

Haggis wrote:You can't stop the chemical reaction. Trickle charge is the way to sustain longer battery life with lead acid once they're fully charged.

I've recently starting getting involved in UPS maintenance for a large Scottish bank, we renew the cells every 5 years regardless.

Hi do u have any for sale?

Jackal

I've got a cheap, 4 years old 110 amp hr leisure battery on my boat.

I leave it connected to a small 5 watt PV panel all year round, done this for the last 2 years and all seems fine when I return to the boat after a few months absence over winter...

Tangata wrote:I've got a cheap, 4 years old 110 amp hr leisure battery on my boat.

I leave it connected to a small 5 watt PV panel all year round, done this for the last 2 years and all seems fine when I return to the boat after a few months absence over winter...

That should work fine.
A 5 watt PV module should in UK winter conditions produce about 0.25 A/H per day into a 12 volt battery.
In order to replace the self discharge losses in a battery it requires an input of very roughly 0.5% of its capacity every day.
For a 110 A/H battery, that is about 0.55 A/H a day.
Your PV module is therefore supplying about half of the theoretical requirement to keep the battery charged, in practice this should should suffice since even if the battery runs down by 0.25% a day, then after 100 days it is still about 75% charged, and by then the days will be longer and the daily input somwhat increased.

No matter how well looked after though, the battery may be approaching the end of its useful life after 4 years.

jackal wrote:

Haggis wrote:You can't stop the chemical reaction. Trickle charge is the way to sustain longer battery life with lead acid once they're fully charged.

I've recently starting getting involved in UPS maintenance for a large Scottish bank, we renew the cells every 5 years regardless.

Hi do u have any for sale?

Jackal

Not yet, but watch this space.