Reviving a 10-year old cordless vacuum. Li-ion battery upgrade. It's alive!

Parts

• 10 x high-drain 18650 Li-ion cells
• 5s Li-ion protection board
• Soft start circuit
• MOSFET (STP80NF55)
• 2 x 100k ohm resistor
• 4.7uF capacitor
• 2 ohm 5W resistor
• 1N5820

I have used a Shark cordless vacuum for 10+ years. After the first few years of intense use. it didn't hold charge any more, so I replaced the battery pack once. The original battery pack is 18v, 12 Ni-MH cells in serial. It costed around $60 or $70.

After another few years of use, I found it needs another battery replacement. But, I didn't feel to spend more money on the old machine, and just put it into the storage for a few years. Actually, while clearing up my storage room recently, I thought I would throw away the vacuum, but I changed my mind and decided to give it another life.

As I said, because I didn't want to spend too much money for the vacuum, I decided not to buy an original replacement battery pack. Instead, I decided to upgrade it to a Li-ion battery pack. However, for a high wattage device like the vacuum cleaner, I needed high-drain Li-ion cells, which usually cost over $5 per cell. Fortunately, I could find cheap Chinese high-drain Li-ion cells for $20 for 10 pack on ebay.

Build a pack: 

Soft start circuit

Pack everything in the shell 

Replaced charger with a 5s Li-ion charger - BTW, the original integrated charging circuit was bypassed, so the charging indicator LED on the handle does not work any more.