Compaq nx9105 power problem

My nx9105 has developed an erratic problem..
Running off mains it may run for several weeks
then the power drops and the battery drains over several hours
Re Plug the power supply in and the power light flashes quickly 10 times
It will then flash more slowly for a seemingly random number of times
Unplug it, leave for a few minutes and plug in again it repeats the cycle, always the 10 fast flashes first.
Eventually, after maybe up to a week it will power up again and recharge the battery

When the light is flashing, it you put an ear by the jack plug oin the rear a high pitched whine is heard like an oscillating charging circuit is working, then when it stops flashing a faint clicking is heard... (Not hard drive clicking!!)

Anyone got any ideas of how to fix this?
Thanks