A battery is made up of cells, usually 1.5 volts, either all joined together in a tin box (think pp3) or in their own boxes grouped together. So my torch here that takes 3xD cells, when they're all in it they're a battery.
Although I'm sure you could have a group of batteries (a battery of batteries?) however what goes in my torch aint flaming batteries!
Dan: my wife teaches English, she has qualifications in teaching languages but is the school librarian (though she's really useful if someone's off). So does most of it from home "on the black" (cash in hand), so if you need any tips...
Edit: my wife despairs when, after she's spent months getting kids to learn the verb "to be", I come in and say "Hi kids, how
is you?". I just tell here it's my language and I'll mangle it how I like
English should be easy, it has almost no cases or genders for a start, although the locals have a hard time with the words "a", "an" and "the", their languages just don't have anything equivalent. The real problem is English is a mix of two languages ( Saxon and Anglo-Frisian (moo) which is a form of German - the "en" of plurals like children and women is very Germanic) so we have at least two words for almost everything, plus some idiot in the dim and distant past decided it would be a good idea to force English into the Latin grammar mould, with hilarious consequences. The pronunciation of vowels has also changed over time, rising higher, although some words have been left behind. We also have too many past and future tenses, much more than anyone in their right mind should actually need. Pronunciation of words has also drifted closer (to, too, two) which also helps muddy the already solifying water. The only good thing is here they're bombarded with English, it's on the telly, in music, computers, advertising... I tell my wife's students they need to watch more telly - "what are you doing?" "Studying".
Go read Bill Bryson's Mother Tongue, it's basically a very funny book about why English is so messed up.