Second battery in Transporter

The Ging and I

I bought a new VW transporter in 07 with a second battery. I travel a lot and mostly have a cooler box for milk/sambos etc.
2 years ago the second battery that feeds the cooler box just boiled up, took me a while to figure where the smell was coming from as the battery is under the seat.
I got a replacement battery fitted when I was next getting a service in VW.
It can not have been the same value battery as it would run flat overnight where the previous one did not. Then it boiled within 16 months from new.
The van was wired by VW as a specification in the factory.
Any thoughts on batteries or just the usual 72Amp ?
Suggestions on why its boiling ?

crabbypaddy

The Ging and I wrote: »

I bought a new VW transporter in 07 with a second battery. I travel a lot and mostly have a cooler box for milk/sambos etc.
2 years ago the second battery that feeds the cooler box just boiled up, took me a while to figure where the smell was coming from as the battery is under the seat.
I got a replacement battery fitted when I was next getting a service in VW.
It can not have been the same value battery as it would run flat overnight where the previous one did not. Then it boiled within 16 months from new.
The van was wired by VW as a specification in the factory.
Any thoughts on batteries or just the usual 72Amp ?
Suggestions on why its boiling ?

Boiling is generally too high charging voltage unless you've got a shorted cell through abuse or manufacturing defect.

Is it boiling on alternator charge or some kind of mains charger. You need to sort that before sacrificing a new battery to a rubbish charger.

Size of the battery depends on what you need to run off it and for how long.

Cooler boxes are generally peltier coolers which are very inefficient they can only cool 16 degrees below ambient temperature, it was about 28 degrees in our van parked in Cashel on saturday, if you were running a coolbox in those conditions the food would have been at 12 degrees and in fact you might be heating rather than cooling the food.

Cooler boxes are generally around 40w so consume about 40Ah per 12 hours. Assuming your 72Ah was brand new and fully charged (lead acid is almost never fully charged) to begin with it would be at 44% charge.

To restore that battery to near full could take 15 hours charging.

The more you discharge your battery the shorter its life you should aim for 50% discharge at most.

Flattening a battery completely will ruin in in jig time especially if left in a discharged state which will cause it to sulfate and turn it into a door stop.

The Ging and I

The Ging and I wrote: »

I bought a new VW transporter in 07 with a second battery. I travel a lot and mostly have a cooler box for milk/sambos etc.
2 years ago the second battery that feeds the cooler box just boiled up, took me a while to figure where the smell was coming from as the battery is under the seat.

Boiling batteries to the point that you can smell the hydrogen is not the healthiest of occupations.

The Ging and I wrote: »

I got a replacement battery fitted when I was next getting a service in VW.
It can not have been the same value battery as it would run flat overnight where the previous one did not. Then it boiled within 16 months from new.

I boil my flooded battery on a regular basis under controlled charge but I replace the electrolyte as needed. My battery is 2 years old and better than new.

The Ging and I wrote: »

The van was wired by VW as a specification in the factory.

Indeed.

The Ging and I wrote: »

Any thoughts on batteries or just the usual 72Amp ?

If 72Ah is going flat overnight then you probably need 150Ah per night.
Depends on the mechanical constrictions and how much power you need to store. 72Ah is only 400Wh usable if that's enough, then it's enough. For camp-site to camp-site it may be adequate, for wild camping I'd say 200-450Ah.

The Ging and I wrote: »

Suggestions on why its boiling?

The usual best ways to boil a battery are;
Over-voltage.
Over-current.
Incorrect charge chemistry algorithm.
Charging a battery with a dead cell.

The best way to kill a cell is to discharge it beyond 50%.

The Ging and I

Ok thanks for your thoughts, I will check it all out.
Its boiling on an alternator charge. Whats confusing me is the main battery has never had a problem or been replaced in 9 years.
Curious Sir L, why you say "indeed" to the van being wired by VW ? Are they bad at this ?
It was on the list of options when I ordered the van.

Macy0161

Would a dodgy alternator not boil the battery quicker than 16 months? I'm kinda expert at fecking up leisure batteries, but that's normally letting them get too low over the winter (I will learn eventually!).

The Ging and I

The Ging and I wrote: »

why you say "indeed" to the van being wired by VW ? Are they bad at this ?

Quite. It's not exclusive to VW but most coach fitters/mechanics.
The setups they install as standard, work by the slimmest definition and the equipment and cable they use is low quality. Funnily enough their speciality isn't charging batteries it's powering loads and floating a battery at a level so feeble it ensures they never boil.
If you want it done right you need to either do it yourself or ask a marine electrician, an electrical engineer, someone living off an off grid electrical system of their own design or a talented free-thinking auto-electrician.

Best you meter the battery post voltage at both batteries while the engine is running and all loads are off, if you get a reading above 14.4v then you need a new alternator or alt. regulator.

Could be it's an AGM battery on a flooded charge set-point. Could also be an unflagged oddball self limiting short-circuit.

Macy0161

Macy0161 wrote: »

Would a dodgy alternator not boil the battery quicker than 16 months?

Yurp it gasses the moment it crosses 14.2V. My battery completes charge at 14.8V + ~0.3V temp compensation.
As to how long it takes to do damage that depends on the level of overcharge, battery condition and chemistry. Flooded being the most tolerant and Gel/AGM the least.

It's actually a healthy thing to do to a flooded battery it keeps the sulphates at bay and saves you having to adapt aggressive tactics like equalisation cycles.
If you were to overcharge a battery by the same amount as it is usually undercharged it to would last much longer.
There is of course an upper limit and it does gas off the electrolyte.
I go through about 250mL deionised H²O a year with my 6 cells.

Filtered rainwater makes a good electrolyte and coolant topper upper.