They differ in 3 of 4 areas
Same tools, so this is about size, weight and cost. No overall winner: pick the size that suits the job.
EnergyThe BSL1850C stores 25% more than the BSL1840M: 90Wh vs 72Wh.
SizeBSL1840M 134 × 83 × 54mm; BSL1850C 97 × 76 × 71mm; BSL1850MA 116 × 76 × 69mm (L × W × H).
ChemistryBSL1840M: Li-ion (cylindrical); BSL1850C: Li-ion (cylindrical); BSL1850MA: Li-ion.
Good to know
Same toolsAll three fit every HiKOKI 18V tool.
Weight0.55 to 0.65kg: too close to call.
Same chargersUC36YSL2 and UC18YKSL charge all three. Charge times are in the specs below.
Energy
BSL1840M
72Wh
BSL1850C
90Wh
BSL1850MA
90Wh
Maker figure, or volts × Ah where they don't publish one. Ah and Wh explained ›
Weight
BSL1840M
0.56kg
BSL1850C
0.55kg
BSL1850MA
0.65kg
Within 0.1kg: too close to call. Full specs
BSL1840MBSL1850CBSL1850MA
Voltage18V18V18V
Capacity4.0Ah5.0Ah5.0Ah
Energy72Wh90Wh90Wh (worked out)
Weight0.56kg0.55kg0.65kg
Energy for its weight129Wh/kg (worked out)164Wh/kg (worked out)138Wh/kg (worked out)
ChemistryLi-ion (cylindrical)Li-ion (cylindrical)Li-ion
Cell type21700 cylindricalNot listedNot listed
Fuel gaugeYesNot listedYes
Size (L × W × H)134 × 83 × 54 mm97 × 76 × 71 mm116 × 76 × 69 mm
Charge time, UC36YSL240 min25 min25 min
Charge time, UC18YKSL2 hr2 hr 30 min2 hr 30 min
Lowest priceNo retailer price yetNo retailer price yetNo retailer price yet
Specs from each maker's own documentation. "Not listed" means the maker doesn't publish it or we haven't found it yet; it never counts as a difference.
Battery guides
Not sure what the numbers mean, or which platform to buy into? Start here.
Power Tool Battery Ah and Wh ExplainedEvery battery gives an "Ah" number: 2.0Ah, 5.0Ah, 8.0Ah. People treat it like a power rating, buy the biggest one they can,…5 Min Read min read ›
Cordless Battery Platforms Explained: Which Should You Buy Into?Here is the thing no one tells you when you buy your first power tool: you are not really choosing a tool.…8 min read min read ›
Corded vs Cordless Power Tools: Which to Buy?Cordless has taken over site and workshop, and for good reason, but corded tools are not dead, and for some jobs they…5 min read min read ›