hey iv got a ansmann acs 67p+ charger that plugs into the wall and i i have a 4000 lrp team power battery

im worried there is sumthing wrong with this new charger becouse on my venom 1800 battery it charges in about 15 mins but with this new battery iv had it charging for times over 25 mins and the green light doesnt come on to say its ready?? it is charging it becouse i can drift with it so wat is with it?/

is it just coz its alot more of a stronger battery that it takes more time??how long should it take to charge?