The XTG-SLRBC solar battery charger is a BARGAIN at only $25! It gains a star simply in versatility to use any AA or AAA battery to charge a device (phone) in an emergency. HOWever, it is a *cheap* charger, so do not get any high expectations (the "price")! If you have the money there are a number of expensive quality units, but the cost vs value of this unit put it at least on par with those those expensive ones.
PROS: Can use any rechargeable AA or AAA battery, easy to replace wore out batteries... ... Charging of batteries can be done solar or by plugging into an USB port. Can use regular alkaline batteries to charge cell phone, iPad, whatever. Built in tester. Reverse polarity protection (reversed installed batteries not charged).
CONS: The solar cells needs over 26 hours to full charge a 4 set of AA batteries (2000mAh each, 8000 total) under full sun (small collecting area, not best solar cells) No indicator for charged batteries (LED only shows it is charging, not very useful) Tester only accurate for Alkaline (voltage 1.5 to 1.6V, while rechargeable is 1.3 to 1.4) Plastic will distort on a cars dashboard (outside air OK, not in car). Easy to scratch/mar the finish. No handy charge estimate on the charger (it is on the packaging)
Again, the COST vs VALUE is excellent simply because compared to most other solar chargers the versatility of this one blows them away. Yes, it is full of flaws, but to make a better one would cost twice as much, to gain about 50% better performance. Under the hood (took it apart) I was impressed with the engineering. A bit crude, but does the job. It has 2 IC chips, an LM324 (Presume for charging batteries) and a SC46166 (high efficiency, and low voltage step-up DC/DC converter, presumably for USB output). My main gripe is the red LED, because it uses what little power from sun to light it up, best not install it. OH, and I would prefer for the USB connections on the other side (under the hinge). All in all an impressive package for $25.