How to have a long Standby and Battery -life?
Regarding this two parts of your question:

...ways to extend the battery life...
...With Wifi/3G -problem, is it possible to have them in some energy -saving mode...

I own a Huawei U8510-1 (Android 2.3.4 Gingerbread) and I also had to deal with that battery issue. When I've bought it, my battery lasted a day, forcing me to recharge it every night.
After some tests, by disabling and enabling stuff, I was able to give it a slight increase, specially when I've disabled the 3G, leaving only the WiFi.
, but couldn't get it to pass two days without a recharge.
The best solution I've found till the present day was this APP:

Easy Battery Saver free

Save power, extend battery life and perfect experience of using phone with Easy Battery Saver!



It works and really makes a difference. I'm able to control every small detail regarding what my phone should or shouldn't be doing, down to what apps can use 3G or WiFi. Now I charge my phone one, max two times a week, depending on the usage. :)