Do mophie juice pack plus cases work well for iPhones?

I bought a used one for $40.

Yeah but you can buy a new one for $35 here: http://gadgetmecrazy.com/index.php?route=product/product&product_id=357&search=juice

but as long as it works!

Mophie works okay with iphone or other cellphones (require a specific case for the specific model). But remember that you'll need to buy a new case every time you upgrade to a new phone or switch to a different phone. I'll say consider battery case only if you are constantly running out of power on phones every single day because you are essentially adding thickness and weight to your iphone all the time and not only when you need extra power.

If you only need to recharge the phone 1-2 times during a day, only need extra power when you use phone for thinks like gaming or watching video, or simply need "emergency" battery power in case you need to recharge, I'd recommend to get a portable power pack (i.e. USB charger). I've used mophie's battery case as well as their USB charger - they are quite pricey and work okay. There are lower cost and high quality alternatives out there. I've bought 2 nextek energy's pocket boost power packs (www.nextekenergy.com) - these work wonderful and costs less than $30.

I've been using the pocket boost 4400 for months now and works wonderful as good as if not better than the mophie power pack I have. I like the anodized aluminum case which matches my iPhone well. I usually just keep it in my bag or pocket and plug it in whenever I need extra power. This way I don't add the extra thickness/weight to my iPhone day in and day out. Perfect solution for my travels, camping trips, bike rides, and day-to-day use.

I've got a red pocket boost micro power pack for my girlfriend and she loves it too. Good to fully recharge iPhone once and in a lipstick size so she just keep it in her purse and plug in when phone battery runs low.

I've got both while on sale at their website www.nextekenergy.com last I checked the pocket boosts are still on sale.