Will this charger kill my battery?

[Neosophist]

A flat battery will draw as much current from a charger as is dictated by its internal resistance. A charger rated as 4 A peak max will only supply 4 amps no matter what the internal resistance of the battery and therefore will not cause any damage. Car battery and quick charge chargers have very high current limits because car batteries are large energy storage devices that may require large current flow to recharge.

This means that when these large capacity chargers are connected to a bike battery with a low internal resistance ie flat, the charging current can be quite a lot higher than is desirable for the small battery structure. This is why manufacturers provide a guide as to the charging requirements for their bike batteries.

4 amps is too high for a bike battery.

Even the 1 hour quick charge as stated on the OP's battery is at 3a/h.

Most battery manufacturers reccomend 0.7 - 1amp hour charge rate.

This is why dedicated bike charges like the optimate et al rarely output a charge current of over 1 amp/h.

[magg]

Neosophist again I agree to disagree but given that the battery in question apparently says 3.0A x 1 hour I cannot see how a charger that has a peak current limit of 4 amps and a continuous rating of 2 amps could do the battery any harm.

A industrial/fast car battery charger is a different matter.

[Neosophist]

My reasonining is quite simple, I have a similar cheap 4/2 charger in the UK, I can't remember the make off hand.. draytek, rytek something or other.

When charging a battery with it the charger will output circa 4 amps until it gets too hot and then it drops down to 2 amps until it cools down.

On prolong charges of large automotive batteries it will even cut out alltogther but thats a different matter.

Since most motorcycle batteries standard charge rate is 0.7 - 1 amp for around 10 hours using 3 amps is an increase from 1amp to 3amp, this is a 200% increase.

Since I don't know how long the charger in question will be capable of outputting 4 amps the worst case scenario is that for the full hour it will charge the battery at 4 amp an hour.

While this extra 1 amp may not seem like much, you have to consider the standard charge is only 1 amp and the fast 1 hour charge at 3 amps is a 200% increase above standard charge rate..

With an extra amp (4ah) your charging at a 300% increased rate over the standard charge as opposed to 200%.

Or 33% above the maximum fast charge rate. (1/3rd)

I wouldn't risk this overcharge on a battery of mine, but it's upto the original owner to try. 1 hour might not be long enough but the plates are quite thin in a bike battery and easily warp and deterioriate with the extra heat produced by excess charging current which in turn shorten the battery life.

I've ruined plenty of batteries in the past by charging them too long or at too high a current. I don't even 'fast-charge' batteries that specify a quick charge time, I just use the slow rate optimate and i've had all my current batteries for 4+ years and they all function fine.

You could sit there and watch the charger for the hour and keep an eye on the amount of amps the charger is outputting either with the built in or an inline ammeter but thats a lot of faffing aroun when you can have peace of mind with a slow rate smart motorcycle charger like an optimate that will provide years of use and allow you to lay the bike up and maintain the battery worry free.

[arsey30]

Most battery manufacturers specify charging at the 10 hour rate, i.e 1/10 of the rated capacity, so a 10a/h would be 1 A, an 8a/h would be 800ma

Charging at very high currents produces more heat that can buckle the plates or give heavy gassing that burns off the electrolyte and lowers the level, more so in unsealed batteries.

Slow charging is best, my modern chargers measure 300ma and 600ma on my multimeter, which I always use to check when using my old 2A charger for a short charge [2 hours], if fully flat and required for imminent use.

So, low current and long charge, high current, very short booster charge. [measure current, check temperature]

[magg]

I still agree to disagree, but everyone needs to do what they are comfortable with.