Caps on or off ?

[BazzaS]

I've a VW Passat whose battery needs charging. I've a Challenge Battery Charger. The Passat handbook says that the battery caps should NOT be removed during charging. The Charger handbook says the battery caps should be REMOVED during charging !
So, who is correct 'cos I'm confused (and is there any danger involved ?)

All advice gratefully received
Regards

 

[JohnD]

if you have a modern maintenance free battery, it should not be necessary to open the caps (and they might be sealed)

If the charger is old the instructions may be expecting an older kind of battery. i am assuming it is a typical domestic trickle charger, 5 amps or so, not a high-power fast-charge one.

 

[BazzaS]

Thanks for the swift response. The battery may be as old as the car (2001) and the caps are not sealed, they are unscrewable to enable distilled water top-up. The charger is brand new with trickle or fast options (I'm using trickle).

 

[Diyisfun]

I would say that if you are having to charge a battery this time of the year, you should think about getting a new one before winter. Unuless you are about to sell the car.

 

[JohnD]

then you may as well loosen the caps to allow any gas pressure to escape. Won't hurt. You may as well top it up too.

When you buy a new battery it probably will be sealed. A good battery can last seven or eight years if not neglected or overcharged.

 

[Ron Gamma]

I'm with JohnD. If you can loosen the caps then do so. It should produce gas in each cell. If it doesn't then you may have found the reason why you need to charge it in the first place.

If the car is low usage and isn't garaged all the time then try one of the solar powered 'battery conditioners' to keep it topped up. You don't need to loosen the caps for this type of charging.

 

[BazzaS]

Thanks to all who replied.
What I can't understand is that when the car is operating normally, the battery caps are on and the battery is being charged via the alternator - why don't all the reasons for taking the caps off when charging via a charger apply?

Anyway its all academic now because I've had to buy a new battery !

 

[TicklyT]

It may be because the voltage regulation on older battery chargers, shall we say, 'left something to be desired'.

About all you got for your money was a transformer, a rectifier and sometimes a switch giving half wave rectification for low charge rate or full wave on high.

As the battery approached a full charge, and the charging current dropped off, so the charger output voltage would go up, possibly to about 20 Volts, increasing the gas production from the cells.

The car electrical system is more closely regulated to about 15 - 16 volts max.