Charger behaviour differences

[Big G]

Charger A I'd had for a few years. It was a advanced charger with a lot of features mainly to do with NiMH's, cycling multiple times and motor run-in, etc. It could charge, but not balance lipo.

Charger B is a new purchase I bought because it would be used on the mains or 12v without the separate adapter needed for charger A. Also it had a built in balancer.

Over my 2 1/2 years of racing I have owned 14 packs of lipo. I've had 5 or 6 of my packs start to bulge in their casing. 1 to the point I could fit it into the durango because it touched the driveshaft and also this 4200mah pack wouldn't recharge more than 3000mah after dumping and hitting the lipo cut off during a race.

Last night I was charging my packs with Charger B and I noticed it's behaviour was a lot different to Charger A's behaviour charging the same pack. Charger A used a CC-CV charging method. It would slowly build up the current over 10-15 secs to 4.5A (4500mah pack) and hold until 8.4V and then slowly the current would drop to 1.0A before saying done. The drop down took probably 10mins give or take.

Charger B will build it's current to 4.5A within 3 seconds and once the voltage has hit 8.4v it will drop to 0A and say done in probably 30 secs.

Had charger A been charging lipo differently (wrongly?) and could possibly be linked to my bulging lipo? It would put a fair few mah into the lipo after hitting 8.4v...

The worst pack I had bulge I bought new and used for 4 or so months when they had a very very slight bulge. I then sold them to my dad who used them for a further 4 months and now they have broken out of their hard case and almost doubled in size... This lipo was barely 8 months old with only 1 race a week on average.

All lipo have been used in buggies on mostly smooth tracks indoors and haven't been off loads of massive jumps. Regularly monitored and balanced when needed.