Had some issues recently that warranted a heap of cranking so i had to put the battery on charge in the garage. Charged it on the 'low' setting (3-ish amps i think), charger gave the green light, battery is sprightly and everything seemed great.

 

Fast forward a couple of days and I was greeted with some intense rotten eggs through my heater blower in the morning... Checked the battery and it isn't venting anything visibly (i.e. any contents spilling out), still works great etc. The alternator voltage regulator is working fine as I checked this as part of my recent issues. I can only assume that this charger overcharged the battery a bit and this is Hydrogen Sulfide venting out the battery from that.

 

The way I park on the drive means that the gas could pool in the battery tray a little (rather than flow down and out through the drain hole in the wing) and then be briefly sucked into the blower through the scuttle. H2S is smelly in low concentrations (before it gets so bad it stops you smelling it.....) so this would make sense.

 

Either way I'm buying a new battery but I'm guessing this charger's over-charge circuit is duff right? I've barely had to use the thing and in my experience 12V chargers are normally pretty bombproof - not a whole lot of circuitry in those things.

 

Battery chargers (for lead acid batteries) usually just work on a constant voltage basis, so naturally reduce charge current as the battery fills. I would guess that the battery is the only thing that has a problem, but measure the output voltage of your charger when connected if you're curious.  What charger model is it?

Its a 'Ring' charger:

https://www.ringautomotive.com/en/product/RCB208

 

I checked the charge voltage briefly when it was on and it seemed fine (can't remember the voltage now off the top of my head though).

I wouldn’t imagine it was a battery charger issue, 3a is quite a small charge amperage wise and you’d have the smell whilst charging if it was overcooking it.

 

if you are getting the smell whilst the car is running it sounds like the alternator could be overcharging. What was the charge voltage with the engine running and revving it up?

 

It should be 14.5v approx max, but that is only a voltage indication, it could be  churning out excessive unregulated amps, a clamp meter is handy for checking the amps figure.

 

Is it a sealed battery or can you remove the caps from the cells? If they are removable check the levels of the electrolyte in the battery, if they are all low you could be looking at an overcharging problem. You can also then check for excess gassing which will create the rotten egg smell and is a sure fire sign of not all being well with the charging system.If it’s sealed this isn’t possible.

 

Most modern chargers are ‘smart chargers ’. I have one of these, which can be left on continuously, which is dead handy when the car is not been used for months.One thing Lead Acid batteries don’t like is being left unused for weeks on end, particularly if discharged.

 

https://www.ctek.com/uk/battery-chargers-12v-24v/mxs-5-0-test-charge-uk

 

Edited 13 December, 20214 yr by mk2tastic

Great, thanks. Haven't noticed the smell any other times than two mornings when starting for the first time and yesterday when i went to pick up a new battery there wasn't a smell at all.

 

I think there are caps for the cells but they're under the sticker (Its a Bosch S4 battery). Can't tell if its just me but it does seem 'sloshier' than the new one.

 

I'll give the alternator a full range of tests before putting the new battery in.

Voltage regulator seems ok - I get ~13.5v with the engine running and all the accessories/lights on, ~13.8v with them all off. No real change with revs either. 0.05v of AC voltage across the terminals when running too. Didn't do a diode test as the battery isn't draining so I'm not worried about a slow leak.

That's rather low, voltage-wise, check connections for cleanliness,  positive cables and earth straps from engine and to battery.

 

Measure with both meter probes at the alternator (positive on output stud, negative on scraped-clean bit of alt body casting); see if the reading is significantly higher there. I'd be happier with something a little north of 14V.