strange battery problem

Hi,

I have an Inspire 7370, I've already contacted Dell Assistance about 7 months ago because my laptop had some severe problems. They changed the parts that weren't working fine and all my pc problems are now resolved, except for one. When I use it without AC adapter and it reaches 60-50% of battery level, it suddenly turns off, after a low battery level warning. Then, if I turn it back on, after skipping the low battery level warning in the bios, the battery level is 1% or 0%. Despite that, the laptop runs smoothly for an addictional 4-5 hours (depending on usage) and then of course it turns off without warning. I've also tried to reinstall windows battery drivers but won't d the trick. Can somebody relate or help? Thanks in advance