I have always used C Tech battery charger, but my older one packet up and I replaced it with another brand charger. I found I had three batteries die after a year or two`s use. I still kept them in my store.
So when I bought a new C-Tech charger I tried it on all three old batteries one being 3 years old. It has rejuvenated all three and I now have three good batteries.
Man these C-Tech chargers are with every penny you pay more for them. Don`t bother fiddling with cheaper crappy chargers Save and only get C-Tech of eBay they are amazing. Hope this can eliminate wasting money for others.
P.S. If you have one don`t be afraid of overcharging your battery, they do switch off when a charge is compleated. Just leave them on for a day or two on an older battery. I even charge my back pack with this charger.