Just watched the YouTube Ice Hole Power tear down of the Vexilar lithium battery. Interesting observation. Vexilar sells and markets the battery as a 9ah and recommends using their SLA (lead) charger which charges at 13.7v. So it quits charging and reads full at 13.7v which will give you 9ah. However... if you had a higher output lithium charger you could get 2-3 more amp hours out of it and essentially have a 12ah battery instead of a 9. I'm guessing Vexilar did this to eliminate multiple chargers and confusion. If you have a Vexilar lithium, it would definitively be worth using a charger designed for a lithium battery. Otherwise it's like going to the gas station and only putting 3/4 of tank in every time. Not only that, but a higher output charger will cut your recharge time in half.
I can add some info to this, because I was wondering the same thing, and yes, I believe you are 100% right.
When I bought my vex lithium last season there was only the standard 410 charger available, same one they have been using for years on standard SLA batteries. In fact, that was the one they were shipping with the battery if you bought the combo. I could run my vexilar for 20 hours or so before that charger would even click on to start a charge cycle on the lithium. Even then, I would usually have to plug it in and turn the flasher on for a second to drop the voltage to trigger the charger. It worked, and when it would take a charge, would charge 5 hours or so.
But then, this season, they came out with two new chargers, both that charge at the higher voltage, and both marketed for their lithium batteries. The fast charging version was on sale locally for the price of the standard charging version, and I bought one. My thinking is, charging up to 100% can only be a good thing as far as performance and more importantly, longevity. Plus, I'd like to be able to plug in a charger after a couple trips out and just charge the thing, not have to wonder if I need to run it another day and hope it will take a charge on the old charger.
I haven't put a timer on my vex and run it on a old versus new charged battery, and I don't plan to. I can tell you this, I charged my battery until the light turned green with the old charger. The next day, I plugged in my new lithium "fast" charger, and it went right to red. I didn't sit and watch it, but it did charge for somewhere between 1.5-2 hours before it went green. That tells me that your 3/4 full is probably pretty accurate, might ben be closer to 2/3 full.
As far as the battery goes, no issues otherwise. On sale for $40 I think it was a pretty good purchase.
