SLAB’s are ok. If you want a cheap supplier try your local “alarm and security” whole saler. I use a company in Hull who supply to trade. A trypical 7Ah Slab is around £9 +VAT
They also sell “matched cells” at a significantly inflated price. Been the nosey type I asked how they match them… Apparantly, all the SLAB’s are thrown onto an analyser charger and the ones that show a capacity figure similar to another get bundled together and sold as matcherd…
Not used SLAB’s recently as I purchased a couple of 4 cell 5Ah li-po’s from hong kong via e-Bay, price £18 each. Very light and mega power
Can now run QRO long time - not many dollar!