battery seems fine but the saw has no power, bogs down immediately in a 2x4

Diagnosis

The Bosch GKS18V-25CN is a high-torque tool, but because it relies on a finite DC power source, it is hypersensitive to "mechanical drag." When a saw bogs down immediately in a standard 2x4 (typically kiln-dried SPF), the issue is rarely the battery's voltage and almost always the friction coefficient at the cutting edge. If the blade is dull, the teeth are no longer shearing the wood fibers; instead, they are pushing against them, creating massive resistance that triggers the motor's electronic overload protection or simply exhausts the current draw. Furthermore, "pitch buildup"—the sticky resin from pine and fir—accumulates in the gullets (the spaces between the teeth). This resin fills the void where sawdust is supposed to be evacuated. When the gullets are full, the blade cannot clear debris, effectively turning the saw into a friction-brake. You can confirm this by inspecting the blade: if the teeth look rounded or if there is a dark, gummy residue coating the sides of the blade, the motor is fighting the material rather than cutting through it.

How to Fix It

To restore the saw's cutting efficiency and reduce motor strain, follow these precise steps to clean and optimize your cutting assembly:

1. Power Down and Safety: Remove the 18V battery pack entirely to prevent accidental startup.
2. Blade Removal: Using the provided wrench, loosen the arbor bolt. Rotate the blade clockwise (opposite of the cutting direction) to break the bolt loose. Remove the blade and the outer flange.
3. Chemical De-Pitching: Submerge the blade in a mixture of warm water and a grease-cutting detergent, or use a dedicated solvent like Simple Green. Let it soak for 15-20 minutes to soften the resin.
4. Mechanical Scrubbing: Use a stiff nylon brush or a brass wire brush to scrub the gullets and the sides of the teeth. Ensure all blackened resin is removed from the tooth faces.
5. Dry and Inspect: Dry the blade completely with a rag. Inspect the carbide tips for chips or rounding. If the tips are rounded, cleaning will not help; you must replace the blade.
6. Reinstallation: Slide the blade back onto the arbor, ensuring the teeth are pointing upward and forward. Tighten the bolt firmly, but do not over-torque, as this can warp the arbor flange.
7. Test Cut: Reinsert the battery and make a shallow "scoring" cut across the top of the 2x4 before committing to a full-depth plunge.

If That Didn't Work

• Switch to a High-ATB Blade: If you are using the factory-installed general purpose blade, switch to a high-ATB (Alternate Top Bevel) blade with a lower tooth count (24T or 30T). High tooth counts are for cross-cutting trim and will bog down instantly in a 2x4 due to lack of chip clearance.
• Check the Shoe Alignment: Inspect the base plate (shoe) for burrs or bent edges. If the shoe is not gliding smoothly on the wood, it creates lateral friction that mimics motor failure. Use a fine-grit sandpaper to smooth any rough spots on the bottom of the shoe.
• Verify Battery Compatibility: Ensure you are using a "ProCORE" 18V battery rather than a standard Core18V if you are doing heavy ripping. The ProCORE series provides a higher discharge rate (Amperage), which prevents the voltage drop that causes the saw to bog down under heavy loads.
• Inspect the Arbor Flange: Check the inner and outer flanges for debris or rust. If the blade is not sitting perfectly flush against the inner flange, it will wobble (run-out), causing the blade to bind in the kerf and stall the motor.

Heads Up

• Avoid "Forcing" the Cut: Never push the saw harder when it begins to bog. This generates heat in the motor windings and can permanently damage the electronic controller. Let the blade do the work; if it slows, pull back.
• Lubricate the Shoe: Periodically apply a small amount of dry PTFE lubricant or paste wax to the bottom of the base plate to reduce friction against the lumber.
• Blade Storage: Store your blades in a dry environment. Humidity can cause micro-corrosion on the carbide tips, which increases friction and reduces the lifespan of the edge.
• Check for "Bowing": If the 2x4 is slightly bowed, it will pinch the blade as you cut, causing an immediate stall. Always cut from the "crown" of the board to avoid the wood closing in on the blade.