Most PVs come with the battery partially charged so you can normally try it out when you first get it, but then I would give it a good charge for like 4-5 hrs. I don't think you need to do the full 8 but you def can.
How much are you vaping? Those batteries are small so they won't last that long before they need to be charged again. If your a heavy vapor you might want to consider a bigger battery PV (over 450mah). That will give you much longer battery life and will allow you to use LR attys/cartos also. Many people like LRs and they give more TH and a warmer vape.
A 3.7V PV will be a huge difference and will allow you to use a wide array of attys/cartos. The Riva, Epower, and kGo are all very nice, inexpensive PVs that will give you long battery life. They all have 510 connections so theres a lot of options to use with them. I started off with a similar slim ecig and now use the EPower now with Ressurector cartos and it's a HUGE difference. The batteries ate 1050mah and last all day.CCV has a really good deal on the EPower too. The Riva is a popular 3.7V too. They have different options for size of batteries, like 650mah, 750mah, etc. LibertyFlights has a good deal on the Riva for a great price. The kGo has an 1100mah battery that lasts a long time. Hoosier ecig supply has a good deal on the kGo and it comes with the big- bore cones. I choose the EPower bc I'm on a budget and its the only one of the three I mentioned that uses non-proprietary batteries. EPower batteries cost $4 compared to Riva/kGo/eGo batteries that are $14-20, and the non-proprietary batteries last a lot longer before they need to be replaced. That was important to me bc I'm a college student who pays for school himself so that and the fact that all parts are replaceable on the EPower, so it keeps costs down. What I like more though is that it's easy to carry a spare battery bc I'm always on the move with work. The batteries are about the size of a AA bit alittle longer so it's easy to always have a spare on you and you can just switch it and have a fresh battery. You get 2 batteries with the kit too so you never have to worry about ever not having a charged battery. With the others bc the battery is part of the unit, you basically have to carry a second PV to have a spare battery with you. It's not that big of a deal, I just don't like having to carry 2 PVs in my pocket.
All are great PVs tho and will def give you the extra oomph and battery life your looking for.
The eGo is also a great PV that many people use and many vendors have it. The eGos are 3.4V instead of 3.7V though, but many people still love them. It's not a huge difference, the 3.7V will give slightly warmer vapor and alittle more TH. they also will handle the lower ohm cartos better though, and that's why I recommend them more for a beginner. A 3.7V will handle the lower 1.5ohm and 1.7ohm attys/cartos with no problems. Those will stress an eGo's mosfet alot and can fry it if your not careful. The 2.0ohm LR cartos work well on the eGo and many people love the Boge 2.0ohm LR cartos on their eGos.
So if your ever looking for more battery life than what you have now, any of these would be a great inexpensive fit.
Goodluck!!