Im going to build a bike with a kit. it will be 48 volt 1000 watt
the kit im looking at says the batterys need to be 48 volt 17Ah
im going to use 4 x 12 volt SLA batteries ( the cheapest way )
my question is : do all 4 batteries need to be 17Ah ? or is it
17Ah total for all 4 batteries ?

Thank you in advance for all the help . I know I should use better
batteries . Maby on first replacement I can get better batteries.
But fir now ill be happy with SLA

These batteries will be connected in series to give the 48 Volts. It is desirable (mandatory?) that they all be the same capacity. The 17Ah is just a suggested size. The number of Ah (or Wh = Volts x Ah) determines how far you can go on a single charge. So if you had 10Ah batteries, you wouldn't have as much range as with 17Ah.

However, I would really question whether you want to lug around 4 x 17Ah SLA batteries on your bike. I would be looking at a 10Ah LiFePO4 pack - which will be much lighter, smaller, and will last much longer with perhaps a slightly lower range on a charge than the 4 x 17Ah SLA's.

Thank you for some very good info dilkes. I will prob go for the LiFiPO4 when it comes time to replace the SLA batteries.
what I realy need to know is do all 4 SLA batteries need to be the same Ah ?? weather they are 10Ah or 17Ah

I read that it would be much more desirable to have matching Amp hour ratings.The lower rated battery will have an adverse affect on the rest. Good luck and enjoy.