Dyson V6 battery question.

[rcrvrp]

Several year old V6 and the original battery just quit taking a charge apparently. Bought a new off brand it it only worked once and them quit. Returned it and got another, same thing, worked good the first time and then would not take a charge.
Wondering if the batteries are bad or if the charger is not working or if its something else. Can anyone here help me? Thanks, RCRVRP