I can't say what the best way to extend the battery's life is, but I charge mine after every second round because the battery meter looks like it won't last a third.
I use it for 3 rounds then it should be about to give up the ghost , not bothered if it conks out mid round as I know my own course well enough to survive without it. Will always make sure it's topped up before playing away though
Its the same sort of battery that most mobiles have in them. They're a lot better than the old style - you had to run them out otherwise they would lose charging ability. The newer Lithium -ion ones don't suffer from the same problem and can be recharged anytime. It still has a finite life of "X" number of re-charges but you probably don't recharge it as often as your phone - how long does a mobile battery last? Ages ....