I have created a device which is actually a powering board or pretty much UPS type. The board designed will work as 6V UPS with batteries. Overcharging and over discharging protection has been added. It can be used in solar powering, as a normal UPS, or as a powering board. 

The board has charging circuit using LM317 which offers overcharging protection also. After that when the source will cut off and work of UPS will start. The battery will discharge and there is over discharging protection circuit which will cut off the power to load if the discharge rate is high. The specific voltage decided here is 6.2V. When two Li-ion batteries of normally 7.4V makes the mark of 6.2V, the load will be cut off. Therefore the battery will cut off when the battery voltage of each Li-ion battery is at 3.15 V approximately. LED is also there to provide visual indication whenever over discharging is detected. This protections are highly necessary in case of battery leak or high discharge rate. The circuit is created while keeping in mind wide selection of batteries which were 2 x 3.7V li-ion batteries. One can also use other batteries.

This protections can easily lower down the maintenance cost of boards like raspberry pi, Arduino, etc. Batteries are often very cheap but when the necessary protections are not used the maintenance cost of boards are added up.

Thus ultimately this is all in one board which will work as UPS and powering device with all types of protection.
The protection provided are:
1. Over charging protection
2. Reverse voltage protection
3. Over discharging protection

We want to hit the market and so we are building an email list. If you like this product and want to back us on Indiegogo, sign up here: https://mailchi.mp/53f46df8b7ad/6vups