I've just had the exact same problem with the wife's Stannah 300 stair lift. I have arrived at the conclusion it is the batteries. Before spending money on new batteries you should be able to prove the fault. My wife has a mobility scooter with two 12V batteries. I used these to wire them in parallel with the ones in the stairlift. Once I did this the stairlift went all the way up no problem. Hence it must be the batteries. I admit you have to know a bit of electrics to try this. You could take a punt and buy new batteries. Out of all the components in theses stairlifts the batteries are probably quite cheap to replace as you can shop around for the best price. Some chap on you tube has posted a really good video on YouTube explaining how to change the batteries and what type you need
Gilly, August 2015
