Change the motherboard battery. These are inserted when the motherboard is manufactured and initially tested. So, even though you say that your laptop is only a year old, the battery could already have been in the board for upto 18 months longer.
I've had a look at the manual for your laptop, and it appears that you need to strip it down in order to gain access to the battery (not very user-friendly, Dell), and as such I would recommend that you get someone with a bit of knowledge to change it for you. If you are careful, you can change it yourself by following the instructions. Coin-Cell Battery Dell™ Inspiron™ 1545 Service Manual