boby

The yongnuo ringlight battery door is available for about $5 and easily replaced.

LFingar Loc: Claverack, NY

With the Canon, and probably the Sunpak, check that the metal tabs at the bottom of the battery well move when you push on them gently with a pen or something similar. These tabs have to be springy to maintain good contact with the batteries and to allow the door to close properly. A build-up of corrosion or debris can prevent movement and make it hard or impossible to close the door.

tovie

It seems that battery chamber doors are not an uncommon problem with flash units. I thank all responders: many worthwhile suggestions. I checked the tabs/springs at the base of both the Canon 420ex and Sunpak units. All are clean and "springy" and there are no signs of battery residue (I only use Duracell). There are no signs that the engagement tabs of the battery well doors are missing or damaged. The battery well doors just won't stay closed when the batteries are inserted. It is possible that the door catches will engage and hold the door in place if the batteries were just 1 mm shorter but I think the easiest solution for me, even though I don't sport a pony tail, is to use elastic, cloth covered pony tail hair retainers for the purpose. Again, many thanx to all you Hogs for the ideas.

Architect1776 Loc: In my mind

Thx

JBRIII

I checked the size of three types of batteries I have, since I mentioned that, all three: energizer lithium, duracell and harbor freight alkaline were the same size within probably .1 mm, contact to contact. I don't have any older carbon cells to see if things have changed over 20 yrs, but since your problem isn't that old, don't think it is battery size. Probably just enough wear somewhere to make things lose, might be door as many suggested (replaceable), but might be in battery holder itself and not so easy to fix, so your solution seems best.

JD750 Loc: SoCal

I have found girth to be a definite result of battery swelling. I have not checked length. There is always a spring on the battery holder so it will accommodate any change in length.

How did you do that exactly? Care is required as putting metal calipers across battery terminals is not advised. So you put a piece of paper in between and subtracted the thickness of the paper?

JBRIII

Yes.
First I checked edge to edge, then as you said terminal to terminal with paper in between. I only thought of the possibility as I have a water proof UV flashlight that uses a weird size battery. Batteries with the same designation were sold but stated to be ~2 mm taller. Took the chance and they work fine, but wondered about AAA, etc. so I checked. My dad once fused a watch band and part of his wrist on a car battery he shorted. Wasn't worried about calipers but exploding? a battery I can live without.

JD750 Loc: SoCal

My buddy went for a test drive without bolting the battery in place. He hit a bump and burnt two thumb size holes in the hood. We kidded him a lot about that!

JBRIII

I don't know if they are commercially available, but there were or are cheap welding units which use or used two car batteries. Lots of power compared to small batteries, but unless I tried/experimented deliberately outside with a long set of wires, I just don't know whether a AA or AAA could melt, catch fire or go boom. As a kid, I took apart C cells to get the electrode for Arc furnances, etc., never had a problem. If now was then, no doubt I'd try the same to get the lithium out, but with I'm sure considerably poorer outcomes.

JD750 Loc: SoCal