I replaced the batteries I'm my mother in laws exterior landscape lights. It specied 600ma NiCd or NiMhs. The store had 800ma NiCd's so that's what I bought. Now after a week they are intermittent at best and prone to all being out after dark.I can get them working and as soon as I turn my back they start going out or go out when I reattacht the light to the base

Do they need more time to charge up? Or is the 800ma the wrong battery? Or something else? Maybe its dirty contacts, but doesn't seem so.
Thanks
Mike