Aegis Max 100W battery issues

Hey guys, new to this forum and new to vaping aswell. Just had a question that I can't really find a proper answer to anywhere else on the internet so I thought I'd ask here. I bought an Aegis Max 100w last week to stop smoking and until 2 days ago it was working great! However I was using the micro-usb port to charge from my phone charger as the guy in the store i bought it from said it would work the same as a dedicated battery charger, starting to think that is not the case. I accidentally left it on charge overnight before work, I didn't think much because the store said this mod has overcharge protection. Ever since then the battery has not been charging properly, or holding charge - usually draining within 10 or so minutes or a few puffs. Bought a dedicated charger today and still the same issue, 2 full batteries yet the mod is having the same problems, 10 or so minutes or a few puffs then flat. When i take the same fully charged batteries out and put them in the dedicated charger it still reads as full. Very confused and just wondering if I've fried my mod or something - hoping this is not the case. No response from the store either.

Any input would be appreciated.
Thanks heaps,
Jacob