Bongo Fury

I was interested to know how quickly the leisure battery would be depleted by my coolbox, so I switched the latter on with the intention of seeing how long it would take for the battery to get to about 11.5v. Then I got distracted (it's an age thing, you know) and forgot all about it until 36 hours later. By which time the Numax was down to 6.8v. I've put it on charge in the rather forlorn hope that it can be saved, but really I know in my heart-of-hearts that poor little batty won't make it through the night. Especially as it's the second time it's been sub-7v.

LB's are designed to go practically flat but with a good charge will be as good as new

dandemann8 wrote:LB's are designed to go practically flat but with a good charge will be as good as new

That's encouraging! Hope you're right. I've got it back up to 12.4 but the little green 'I'm alive and well' indicator hasn't popped it's head up yet

You will probably get away with it as it was not left discharged for too many days. being left flat is normally death to lead acid batteries, especially the smaller sealed gel type.

Give it a few charge/discharge cycles and you should get your green indicator back.


Frank

dandemann8 wrote:LB's are designed to go practically flat but with a good charge will be as good as new

That's not true at all. They are designed to self-discharge more slowly. If you flatten them (below 10.5v) the plates will start to sulphate like any lead acid battery. But, as said above, if you deal with it fast you should limit the damage (you "de-sulphate" the plates by charging - if left for a while you get crystals which won't "de-sulphate" at all) , but I'm afraid, you will have done some damage.

not my description!

"Leisure batteries and car batteries both make use of lead acid technology. That is to say they are both plastic boxes that contain rows of interconnected rectangular flat lead plates and a mix of sulphuric acid and water.

The main priority of a car battery is to provide starting power for the vehicle. In addition it will provide a stable flow of power for the car electrical systems. A car battery cannot be allowed to remain far below 'full charge' for any length of time without physically degrading and permanently losing performance.

The main priority of a leisure battery is the flow of power with engine starting coming secondary to that. Some leisure batteries are not actually designed for starting engines while others have both capabilities.

The internal structure of a car battery contains many, thin lead plates. The surface area* of all of these lead plates combined allows for the strong boost of power required to start the car engine.

By contrast a leisure battery contains fewer plates, each of which is physically thicker.

Each lead plate, when submerged in sulphuric acid and water is capable of storing and releasing energy. A thick plate will release its energy slowly. A thin plate will do the opposite.

Over the past century car batteries haven't changed much in their basic design. Engineers, by experimenting with different numbers of lead plates, different sizes and thicknesses, managed to create lead acid batteries for specific jobs.

So why do leisure batteries tolerate being fully discharged and why do car batteries not?

The chemical reaction between the acid and the lead plate causes atoms known as electrons to jump from the (+) plates to the (-) plates. In doing so the basis of electricity occurs.

When a car battery stands for a period of time without recharging, the thin lead plates minus their electrons will sulphate and degrade. Their performance will be reduced permanently.

Thicker plates, because of their smaller surface area* rarely lose 'too many' electrons and will not suffer the same level of destruction via sulphation. This means that a leisure battery can stand being fully dis-charged and will ultimately power your caravan appliances for a good deal longer before needing replacing."

Julian

I see. I understand the lesser surface area principal - that makes perfect sense. So as long as your leisure battery really is a proper leisure battery (i.e. with thicker and fewer plates) then you do indeed have a better level of total discharge protection.

Saying that , it still kills them if left flat for long periods. My friend's LB is a good example. New in. Used 'till flat 3 or 4 times on 1 year. Left flat over winter. Useless the next spring.

The term that should be used is surface area to volume ratio. An sb and an lb may have broadly similar surface areas, but due to its thicker plates the lb will have a much lower sa/vol ratio. And this (I reckon) is what will give it strength in depth. But there is still (I would think) the issue of surface coating and its effect on battery efficiency?

dandemann8 wrote:LB's are designed to go practically flat but with a good charge will be as good as new

Not so, leisure batteries lose life significantly when allowed to fall below 50% charge, the good news is that the occasional heavy discharge can be recovered from with a good long trickle charge most times if the battery is in otherwise good condition. Put the battery on charge and keep it on for 2 days or more before even trying to see if it has recovered. If you want to try seeing how long you can run a device get one of those battery protection devices that cut out when the volts fall too low.

To maximise the LB life ensure it does not fall below 50% charge, recharge it asap and regularly use a multistage charger