Your batteries are starting to degrade, but the good news is they're still holding a charge for a week, so you really don't need to rush to replace them at this point.
The flickering of the charged indicator is normal, as the shaver is still plugged in and the batteries are fully charged. The flickering is due to the batteries chemicals breaking down, and as such, the charge cycle keeps "topping" them off while it's still plugged in.
When you finally aren't able to get a decent amount of cordless operation and run times from your shaver, then you'll want to get them replaced, whether you decide to do that yourself or have it done by a professional service center, is up to you.
Here's a reference for your future use.
www.electricshaver.com carries replacement (factory OEM) batteries for most brands of shavers and they also will provide the repair/replacement service for you, should you decide you don't want to do it yourself. You can also give them a call at 1-888-476-1785 and request a price quote, etc.
Anyway, your shaver is working fine and all you need to do is make sure you're not letting the shaver stay plugged in and charging constantly for more than a day, since any "extra" chargind isn't doing anything except keeping the batteries at a constant state of charge. Heat is a byproduct of charging and discharging any battery and as such, you want to allow for a cool down period before recharging them.
I tend to use my shaver until it is almost completely discharged before recharging it. By doing this, you can get the longest working life out of your batteries before you'll have to replace them.
Hope you find this Very Helpful and best regards!