I found an easy way to charge an M401 battery on DSE901 or RN4075 charger. See picture. I've jammed a plastic q-tip shaft between the battery and charger case to make the battery touch both contacts on the charger. The M401 is slightly thinner than the DSE so it won't thread in at all, but by holding it in crooked like this it will charge the battery just fine. The charge rate and voltage is the same on both chargers, no no worries on over/undercharging. Pretty handy if you have more than one dead battery and only one charger. I barely touch my DSE e-cigs at all after getting the m401 so now I'm never short of chargers. 3 m401 batteries, 3 chargers.
I imagine this would work with a DSE901 battery and a penstyle charger, but I have no penstyle chargers to test that theory.
I imagine this would work with a DSE901 battery and a penstyle charger, but I have no penstyle chargers to test that theory.