# Can I make my Battery Pack Much Efficient in my DIY Power Bank?

I was having a project of a DIY power bank as a backup for my phone. I need to use super thin batteries for this application. my goal is to make this power bank as efficient as possible. now I want to charge this power bank with a USB-C connector which at minimum will be able to provide 3Amps of current. My idea to make this Power Bank is to use 6 Small 950mAh Batteries which adds to a total of 5700mAh. as my goal is to be efficient, I am going to use one of the batteries to power the output and the others charging up or being idle. the 6 batteries will be charging with 2S3P Configuration so that it charges with 8.4V and 3A Minimum. but when the charging is complete it needs to change its configuration to 6S1P Battery pack and stay idle. and when the battery that is used to power the output starts to drain out it will be sent to charging and one of the charged-up batteries will be powering the output.

When the Battery 1 & 2 is powering the output

and When Battery 1 & 2 are drained

and the cycle repeats. now my question is can we change the batteries from series or charging or idle state to outputting state with some kind of electrical system that I can change with an Arduino. it can be any electrical system expect Relays (because it drains the batteries quicker when they are turned on).

• Why do you believe switching between different configurations has a positive effect on efficiency? And no getting 3A minimum from Type-C is not true, it depends on the charger how many amps of current or watts of power it can output, and not all chargers can output 3A with the voltage you want. How do you intend to negotiate the voltage, and what will be charging the battery from Type-C power supply? Commented Apr 15 at 17:48
• The minimum a Type-C Connector can output is 3A so that i can have any kind of charger that can do 9V Power Delivery. It makes it free that we don't need to find an exact 5A Charger Commented Apr 17 at 19:21
• Sorry but even if the Type-C connectors have a requirement for 5A rating, and standard Type-C cable assemblies have a requirement for 3A rating, it doed not mean your charger can output 3A. It is perfectly allowed for a device to output only up to 1.5A or just the bare minimum of 0.9A. You cannot assume you get 3A minimum, and you must only draw what the supply says is available. You cannot get 5A without PD negotiation and E-marked cable, and you are allowed to draw up to 3A if the supply signals you it can provide 3A. Commented Apr 17 at 19:41